The present invention pertains generally to the fabrication of semiconductor devices and more specifically to systems and methods for etching materials during formation of on the semiconductor devices.
Etching processes are used to selectively remove portions of materials deposited or grown on a semiconductor wafer. After a feature is patterned on a layer formed on the semiconductor wafer using photolithographic tools and process, etching processes are used to transfer the patterned feature to materials subjacent a photoresist layer. Etching processes employed in the fabrication of semiconductor devices generally fall into two categories: wet and dry.
In either process, a layer of material, either a metallization layer or a dielectric layer, is exposed to an etchant, which chemically reacts with materials of the layer. The chemical reaction between the etchant and layer material removes an estimated predetermined portion of the layer material to form a patterned feature such as a portion of a semiconductor device. Depending on the type of etchant and etch process, the amount of layer material removed by the etchant may be controlled by reaction temperature and pressure, and etch time. During a wet etch process, the wafer on which the semiconductor device is being formed is immersed in a tank containing the etchant for a predetermined time. The device is then rinsed to remove acids, other reaction by-products and contaminants. The wafer is then dried.
Wet etch processes etch materials in all directions at substantially the same etch rate, i.e., isotropically, and are typically limited to the larger feature sizes above 3xcexc. Wet etch process tend to undercut features that require only a minimum lateral etch. Moreover, cross contamination from wafer to wafer, or batch-to-batch is an inherent problem in wet etching.
Dry etching provides an alternative to the isotropic characteristic of a wet etch process. Dry etch processes do not etch materials in a lateral direction, i.e., anistropic etch. Accordingly, dry etching is used for the fabrication of smaller features below the acceptable size limits for wet etch processes. Dry etching refers generally to those etch processes in which gases, including a plasma form, are the etch medium.
In the dry etch process, plasma-enhanced atomic species bombard the layer material to remove the estimated predetermined portion of the surface of the material. A chemical reaction, or ionic milling, takes place in a reaction chamber at sub-atmospheric pressures. One or more wafers are positioned on a platen within the reaction chamber, and an electronic bias is applied to the platen and/or wafer via an RF power source or that is induced by the plasma. In some cases, a second power source, such as an electrode or cathode coil, generates a plasma region adjacent the surface of the semiconductor device. A reactant gas introduced into the chamber is ionized within the plasma, and the resultant ions physically remove surface material of the layer by chemical reaction, or by physical bombardment, depending on the type of plasma-generating system used.
While dry etch processes provide advantages over wet etching in the fabrication of smaller features, etch selectivity in dry etch processes is difficult to control with certain materials and etching conditions. Moreover, features with higher aspect ratios cause etching to slow at the bottom of the feature; therefore, over-etching is required to clear stringers on the vertical dimension of the feature, even after the bottom of the feature is etched to desired thickness. Moreover, the plasma generating systems are expensive to purchase and maintain.
The present invention provides a method for dry etching a semiconductor device that isoptropically etches a material on the semiconductor device. In this manner, the present method for dry etching may be used without the need for over-etching. In addition, the present invention avoids the inherent contamination problems and additional drying steps necessary in wet etching processes, and the expense of the plasma-generating systems necessary for typical dry etch processes.
As used hereinafter, the term xe2x80x9csemiconductor devicexe2x80x9d may mean a wafer substrate (also referred to as a xe2x80x9cdevice substratexe2x80x9d) having one or more layers or films formed thereon for the fabrication of integrated circuits or may mean an individual device, such as a transistor, created by the fabrication process, depending on context. The term material as used to describe the invention shall mean any type of material deposited, and/or grown, on a wafer substrate in fabrication of the semiconductor device. Such materials may include, but are not limited to, metals, metal alloys, dielectrics, insulating materials, photoresist materials, masking materials, etc. In addition, any reference to deposition of a material shall include any method of forming a layer or film on a semiconductor device. For example, xe2x80x9cdepositing a materialxe2x80x9d may be used interchangeably with xe2x80x9cgrowing a materialxe2x80x9d on a semiconductor device.
With respect to the present invention, the material is typically deposited on the device substrate in the form of a layer or film having a known thickness. In order to etch the material, a featured is patterned using photolithography processes and photoresist materials known to those skilled in the art. The semiconductor device is then positioned within a reaction chamber. A sufficient amount of the etchant gas is introduced into the reaction chamber to etch at least a portion of the material to a predetermined thickness, and consistent with the patterned feature.
The interior of the chamber is preferably maintained at a predetermined temperature and predetermined pressure to facilitate a chemical reaction between the etchant gas and material. In an exemplary embodiment, a halogen-based etchant gas may be used to remove at least a portion of a refractory metal film. The halogen-based etchant may comprise hydrogen bromide, or any one of the methyl bromide species. The refractory metal may comprise tungsten, tantalum or titanium based metal film or metal alloy film.
The present invention is distinguished from prior art dry etch procedures by the use of an etchant gas that is chemically reactive with the material without need for generating a plasma in the reaction chamber or without providing an electrical bias to the semiconductor device.